The proliferation of digital recording media has enabled many people to enjoy content, such as for example films and music, with, at least in theory, no deterioration of quality over time. Unfortunately, it has also offered possibilities for pirating, since pure digital content may be copied quite easily an unlimited number of times. In order K to counter this, many different solutions as to how to protect digital content have been proposed.
Digital Versatile Disks (DVDs), which make up a great part of the sold media, for example use static storage. To prevent illegal copying, the digital content on DVDs is encoded using the Content Scrambling System (CSS) algorithm. The key used for encoding is dedicated and a corresponding key, used for decoding, is common to every player of a manufacturer.
Players for more recent pre-recorded media, such as the ones protected by the Blu-ray Disc Copy Protection System (BD-CPS) and Content Protection for Pre-recorded Media (CPPM), each have one unique set of keys. Protection is based on broadcast techniques, such as for example the Fiat-Naor scheme.
There have also been attempts to turn a static medium into a dynamic one by adding a processor to the recording medium. Japanese patent application 10-242555 teaches a CD-ROM with an embedded secure processor that communicates with the player. The processor forwards a password to the player, the password allowing decryption of the content. This solution, however, is susceptible to replay attacks.
Another Japanese patent application, 10-050713, discloses a system that uses a recording medium with a built-in IC chip, which holds the decryption key for the content. The IC chip passes the key to the host only upon successful authentication of the host, and adds a counter to limit the number of times the key may be transferred. This solution does not, however, prevent a pirate from creating counterfeit titles. Furthermore, if a pirate manages to build a fake player, he can use techniques that discloses the decoding key.
It can therefore be appreciated that there is a need for a flexible solution that overcomes problems of the prior art and improves the security of pre-recorded digital media. This invention provides such a solution.